In numerically controlled cutting machines used today, machines are usually programmed by tape to perform certain specified operations upon a workpiece in a certain preprogrammed sequence. Due to the repetitive nature of the work, a reference dimension is programmed into the machine on the tape and this reference dimension is usually a certain given distance from a datum point on the machine to the actual cutting point of a machine tool.
This cutting point may rest on any one of several differently configured cutting inserts depending upon the cutting operation to be performed. However, it is the case that the dimension of the cutting point from the datum plane of the cutting machine must always be maintained to a very precise degree in order to hold the workpiece within the required tolerances of manufacture.
Since most numerically controlled cutting machines use the replaceable type cutting inserts of varying configurations, there is a difficulty in maintaining the precise dimension mentioned above when interchanging cutting insert configurations or replacing cutting inserts when they have become worn.
One of the ways in which this difference in dimensions may be corrected is to reprogram the tape in the numerical controlled machine when the reference dimension to the cutting point changes due to a change of the actual cutting tool itself.
A preferable way to compensate for the change that may be introduced with a new cutting tool is to have a structure that allows adjustment of the reference cutting point with respect to the shank of the cutting tool that is supported by the numerical controlled type machine.
It is an object of the present invention to provide an adjustable tool unit in a boring bar head so that, as tool units are interchanged in the head, the cutting point may be readjusted to agree with the dimension programmed on the tape of the numerical controlled machine.
It is a further object of the present invention to provide a tool unit that, while being adjustable, is also firmly supported and held during the actual cutting operations.
It is still a further object of the present invention to provide a structure that will accomplish the above objects and yet may be provided in some of the smaller boring bar shanks that are required to do machining in a very small bore of a workpiece.